There are several opposing schools of thought about whether dogs need a coat, and below is the post I feel sums it all up the best. Although it may seem like common sense, I just need to add one thing: If a dog coat is not water resistant, don't use it when it's snowing. Also, Gatsby's personal choice in coats is Ruff Wear. http://www.ruffwear.com/
Copied from Does My Dog Really Need A Coat?
February 24th, 2009 by Dan
While you may think that a dog’s natural fur coat is enough protection against the elements, this isn’t true for every individual canine. While some dogs (Siberian Huskies, Samoyeds, Great Pyrenees, Saint Bernards, etc) have thick fur that is designed to keep them warm in cold temperatures, others would be more comfortable with an extra layer.So which dogs *do* need coats?:-
Dogs with very short fur (Pit Bulls, Boxers, Dobermans, etc) can all benefit from wearing a coat due to their lack of insulating fur.*
Dogs with little body fat (Greyhounds, Pharaoh Hounds, Italian Greyhounds, etc) that can’t retain heat as well as their stocky canine cousins should wear an additional of insulation in cold or wet weather.*
Toy breeds that can’t retain heat as well as larger dogs and will be more affected by the cold.*
Elderly dogs or those who are suffering from illnesses. Keeping warm puts extra stress on a dog’s system. A coat allows them to preserve their energy.*
Dog’s that are accustom to warmer weather and are then brought to a cold region may need an extra layer as they are not acclimated to the new climate.*
Any dog that is hesitant to go outside in the chilly weather or shows obvious signs of being cold while you’re outside (shivering) will probably be more willing to spend time outdoors if they are wearing a coat.
Keep in mind that if a healthy dog is actively exercising in cold weather that he probably won’t need a coat for his entire time outside. However, if you’re just going for a leisurely walk, a coat will keep your dog more comfortable.